We need to get a few lingo s sorted in order to understand the situation. There is no such thing as a thunderbird account. Thunderbird is the program. So you would have created mail accounts for each of your email addresses to download emails which you can view via Thunderbird. re ''I created a contact list or mailing list.'' In Thunderbird there is an 'Address Book' It has some default address books eg: 'Personal address Book', but you can also create some of your own. Address books hold contacts. The contact is added to an address book, but they can also be selected to appear in any number of Mailing Lists and look like a sub list to an address book. Mailing Lists are specifically used for sending one email to a group of people. So perhaps you need to explain how you created the list of contacts. Did you create them in thunderbird's Address Book? If no: What program did you use to create that list? Did you use MSWord or perhaps MSExcel and created an *.csv file ? re :'' I shared this with another thunderbird account'' You can have many email addresses set up in the one profile and they all use the same address book. I've already explained that there is no such thing as another thunderbird account, so perhaps you are talking about someone on a completely different computer who also uses Thunderbird program to access their emails. How did you share the list of contacts with the other person?